Electrolyte composition for electrolysis of brine, method for electrolysis of brine, and sodium hydroxide prepared therefrom

ABSTRACT

The present invention relates to an electrolyte composition for electrolysis of brine, a method for electrolysis of brine, and sodium hydroxide prepared therefrom, and particularly to an electrolyte composition for electrolysis of brine, a method for electrolysis of brine comprising injecting brine and pure water respectively to a cation chamber and an anion chamber divided by a separation membrane installed in an electrolytic cell through a brine injection tube and a pure water injection tube, and applying a power source to an anode plate and a cathode plate installed in the cation chamber and anion chamber to separate produced chloride gas, hydrogen gas, and a sodium hydroxide aqueous solution characterized in that an aqueous solution of a platinum compound is injected into the anion chamber through the pure water injection tube, and sodium hydroxide prepared therefrom.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is based on Korean patent application No.2002-0016970 filed in the Korean Intellectual Property Office on Mar.28, 2002, and Korean patent application No. 2002-0018673 filed in theKorean Intellectual Property Office on Apr. 4, 2002, the contents ofwhich are incorporated hereinto by reference.

BACKGROUND OF THE INVENTION

[0002] (a) Field of the Invention

[0003] The present invention relates to an electrolyte composition forelectrolysis of brine and a method for electrolysis of brine and sodiumhydroxide prepared therefrom, and particularly to an electrolytecomposition for electrolysis of brine and a method for electrolysis ofbrine which minimize electric resistance of an electrode plate and thuscan reduce power consumption, do not require separation of anelectrolytic cell by interrupting electrolysis in order to replace anelectrode plate and thus makes electrolysis efficient, and which canreduce the cost required for maintaining and repairing an electrolyticcell and thus can economically prepare sodium hydroxide, and sodiumhydroxide prepared therefrom.

[0004] (b) Description of the Related Art

[0005] Sodium hydroxide (NaOH) is a pure white solid, and its aqueoussolution shows strong alkalinity. Sodium hydroxide is a widely usedmaterial for preparation of pulp, fiber, dye, rubber, soap, etc., and iswidely used for a desiccant because it has a strong deliquescingproperty.

[0006] Methods for preparing sodium hydroxide include a Leblanc processthat prepares sodium hydroxide by adding sulfuric acid to crude salt tocause thermolysis, an ammonia soda process that prepares sodiumhydroxide by reacting soda lime with Ca(OH)₂, and an electrolysisprocess that prepares sodium hydroxide by electrolyzing brine, etc.Presently, the electrolysis process is the most widely used, and itincludes a diaphragm process, a mercury process, and an ion-exchangemembrane process.

[0007] A diaphragm process prepares sodium hydroxide by installing adiaphragm made of asbestos between a graphite anode and an iron cathodeso that chlorine coming from the anode may not react with sodiumhydroxide coming from the cathode, and a mercury process prepares sodiumhydroxide using mercury as a cathode material. However, the diaphragmprocess has a problem of practical use because the concentration ofsodium hydroxide prepared is merely 10 to 13%, and thus theconcentration processes must be repeated several times. The mercuryprocess is not presently used because of environmental contaminationproblems of the heavy metal mercury.

[0008] An ion-exchange membrane process is most widely used, in which anion-exchange membrane is installed inside an electrolytic cell to dividethe electrolytic cell into a cation chamber and an anion chamber withbrine as an electrolyte, an anode plate and a cathode plate arerespectively installed in the cation chamber and the anion chamber, andelectric power is supplied to the two electrode plates to obtainchlorine gas from the anode and hydrogen and sodium hydroxide from thecathode.

[0009]FIG. 3 is a cross-sectional view of an apparatus for electrolysisof brine by an ion-exchange membrane process. As shown in FIG. 3, anelectrolytic cell (11) is comprised of a cation chamber (12) and ananion chamber (13), and a membrane (14) dividing the cation chamber (12)and the anion chamber (13) is installed therebetween.

[0010] To the cation chamber (12), brine is injected through a brineinjection tube (15), waste brine that remains after reaction andchlorine gas produced during electrolysis are stored in an cationchamber discharge tank (17) after passing through a cation chamberdischarge tube (16), chlorine gas is discharged again through a chlorinegas discharge tube (18), and brine that remains after reaction andunreacted brine are discharged through a waste brine discharge tube(19).

[0011] Pure water is injected into the anion chamber (13) through a purewater injection tube (20), and a sodium hydroxide aqueous solution andhydrogen gas, reactants produced in the anion chamber (13), are storedin an anion chamber discharge tank (22) after passing through an anionchamber discharge tube (21). Hydrogen gas is discharged again through ahydrogen gas discharge tube (23), and the sodium hydroxide aqueoussolution is discharged through a sodium hydroxide aqueous solutiondischarge tube (24).

[0012] The cation chamber (12) and the anion chamber (13) arerespectively equipped with an anode plate (25) and a cathode plate (26).

[0013]FIG. 1 shows a chemical equation involved in electrolysis of brineby the existing ion-exchange membrane process. As shown in FIG. 1, aselectrolysis proceeds, hydrogen ions remaining in an anion chamber areattached to a cathode plate surface to increase electric resistance of acathode plate, thereby increasing power consumption during electrolysis.

[0014] Generally, in order to restrain the increase in resistance of anelectrode plate, the electrode plate surface is previously coated orplated with compounds such as AuCl₃, RuCl₃, IrCl₃, etc., or it is firedat 400 to 500° C. and inserted into an electrolytic cell. Ifelectrolyzing brine by the above method, compounds such as AuCl₃, RuCl₃,IrCl₃, etc. coated or plated on the electrode plate surface will becontinuously oxidized to continuously increase electric resistance ofthe electrode plate surface. Therefore, there is a problem that inproportion to the increased electric resistance, more power is consumedin electrolysis and the production cost of sodium hydroxide increases.

[0015] In order to overcome these problems, the ion-exchange membrane isreplaced every 2 years, the cathode plate every four years, and theanode plate every 6 years, or compounds such as Au, Ru, Ir, etc.attached to the electrode plate are removed and compounds such as AuCl₃,RuCl₃, IrCl₃, etc. are coated or plated again on the electrode plate torenew it. However, the renewal of an electrode plate requires much timeand human and material resources, and the electrolytic cell cannot beoperated during the time required for renewal, and thus productivity isreduced.

SUMMARY OF THE INVENTION

[0016] The present invention is made in order to solve the problems ofthe prior arts, and it is an object of the present invention to providean electrolyte composition for electrolysis of brine comprising anaqueous solution of a platinum compound that minimizes electricresistance of an electrode plate and thus can reduce power consumption,that needs no interruption of electrolysis to separate an electrolyticcell in order to replace an electrode plate and thus makes anelectrolysis process efficient, and that can reduce the cost requiredfor maintenance and repair of an electrolytic cell to thus economicallyprepare sodium hydroxide.

[0017] It is another object of the present invention to provide a methodfor electrolysis of brine that injects the electrolysis composition forelectrolysis of brine comprising an aqueous solution of a platinumcompound into an electrolytic cell to prepare sodium hydroxide.

[0018] It is another object of the present invention to provide sodiumhydroxide prepared by the above method.

[0019] It is another object of the present invention to provide anapparatus for electrolysis of brine.

[0020] In order to achieve these objects, the present invention providesan electrolyte composition for electrolysis of brine comprising anaqueous solution of a platinum compound.

[0021] The present invention also provides a method for electrolysis ofbrine comprising injecting brine and pure water respectively into acation chamber and an anion chamber divided by a separation membraneinstalled inside an electrolytic cell through a brine injection tube anda pure water injection tube and applying a power source to an anodeplate and a cathode plate installed in the cation chamber and the anionchamber to separate produced chlorine gas, hydrogen gas, and sodiumhydroxide aqueous solution, characterized in that an aqueous solution ofa platinum compound is injected into the anion chamber through the purewater injection tube.

[0022] The present invention also provides sodium hydroxide prepared bythe above method.

[0023] The present invention also provides an apparatus for electrolysisof brine comprising a cation chamber and an anion chamber divided by aseparation membrane installed in an electrolytic cell; an anode plateand a cathode plate equipped in the cation chamber and the anionchamber; a brine injection tube connected to the cation chamber; a purewater injection tube connected to the anion chamber; and a platinumcompound aqueous solution injection tube connected to the pure waterinjection tube.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 shows a Chemical Equation involved in electrolysis of brineby an ion-exchange membrane process.

[0025]FIG. 2 shows a Chemical Equation involved in the electrolysis ofbrine of the present invention.

[0026]FIG. 3 is a cross-sectional view of an apparatus for electrolysisof brine by an ion-exchange membrane process of the prior art.

[0027]FIG. 4 is a cross-sectional view of the apparatus for electrolysisof brine of the present invention.

[0028]FIG. 5 shows operating voltages of the electrolytic cells ofExample 6 and Comparative Examples 1 to 3 with the lapse of operationtime.

EXPLANATION OF REFERENCE NUMERALS IN FIGURES

[0029]11, 111: Electrolytic cell

[0030]12, 112: Cation chamber

[0031]13, 113: Anion chamber

[0032]4, 114: Separation membrane

[0033]15, 115: Brine injection tube

[0034]16, 116: Cation chamber discharge tube

[0035]17, 117: Cation chamber discharge tank

[0036]18, 118: Chlorine gas discharge tube

[0037]19, 119: Waste brine discharge tube

[0038]20, 120: Pure water injection tube

[0039]21, 121: Anion chamber discharge tube

[0040]22, 122: Anion chamber discharge tank

[0041]23, 123: Hydrogen gas discharge tube

[0042]24, 124: Sodium hydroxide aqueous solution discharge tube

[0043]25, 125: Anode plate

[0044]26, 126: Cathode plate

[0045]127: Platinum compound aqueous solution injection tube

DETAILED DESCRIPTION AND THE PREFERRED EMBODIMENTS

[0046] The present invention will now be explained in detail.

[0047] The present invention is characterized by adding a platinumcompound to an electrolyte composition for electrolysis of brine,particularly in an aqueous solution phase. The platinum compound ispreferably selected from hexachloroplatinate (IV) (H₂PtCl₆. 6H₂O),potassium tetrachloroplatinate (II) (K₂PtCl₄), diaminodinitroplatinum(II) (Pt(NH₃)₂(NO)₂), hexaaminoplatinum (IV) chloride (Pt(NH₃)₆Cl₄),tetraamine platinum (II) chloride (Pt(NH₃)₄Cl₂), hydrogenhexahydroxoplatinate (IV) (H₂Pt(OH)₆) and sodium tetrachloroplatinate(II) (Na₂PtCl₄. 6H₂O). Hydrogen hexahydroxoplatinate (IV) (H₂Pt(OH)₆),separated into platinum ions, hydrogen ions, and hydroxide ions in anaqueous solution, is most preferable.

[0048]FIG. 2 shows a chemical equation of electrolysis of brine whenhydrogen hexahydroxoplatinate (IV) is introduced into an electrolyticcell. Saturated brine is injected into a cation chamber, and pure waterand a platinum compound aqueous solution are injected into an anionchamber. In the present invention, the liquid mixture of the pure waterand the platinum compound aqueous solution is referred to as anelectrolytic composition for electrolysis of brine.

[0049] As shown in FIG. 2, Pt⁴⁺ platinum ions in the platinum compoundaqueous solution move to a cathode plate surface. Platinum ions havesuperior electrical conductivity and corrosion resistance for strongalkali. In addition, a cathode plate plated with platinum ions hascomparatively low electric resistance compared to a cathode plate platedwith a material other than platinum ions or an unplated cathode plate,and it also has strong corrosion resistance to a strong alkali sodiumhydroxide aqueous solution produced in an anion chamber and thus canprevent corrosion of a cathode.

[0050] The contents of platinum compounds in the platinum compoundaqueous solution are preferably 0.1 to 10 wt %. If the contents are lessthan 0.1 wt %, an increase in electric resistance of a cathode platesurface cannot be prevented, and if the contents are more than 10 wt %,power consumption will not be simply proportional to the contents of theexpensive platinum compounds, thus making it uneconomical.

[0051] In addition, the amount of the platinum compound aqueous solutionin the electrolyte composition for electrolysis of brine of the presentinvention comprising an aqueous solution of the platinum compound ispreferably 0.1 to 0.2 liter per 1 liter of pure water injected into ananion chamber. If the amount is less than 0.1 liter per 1 liter of purewater, the amount of prepared sodium hydroxide will be small, and if theamount is more than 0.2 liter, electric resistance of an electrode platewill not decrease in proportion to the amount of expensive platinumcompounds, thus making it uneconomical.

[0052] The method for electrolysis of brine of the present invention,which comprises injecting brine and pure water respectively into acation chamber and an anion chamber divided by a separation membraneinstalled in an electrolytic cell through a brine injection tube and apure water injection tube and applying a power source to an anode plateand a cathode plate installed in the cation chamber and the anionchamber to separate produced chlorine gas, hydrogen gas, and sodiumhydroxide aqueous solution, is characterized in that an aqueous solutionof the platinum compound is injected into the anion chamber through thepure water injection tube.

[0053] An apparatus for electrolysis used in the electrolysis method ofthe present invention will be explained referring to FIG. 4. FIG. 4 is across-sectional view of the apparatus for electrolysis of brine of thepresent invention.

[0054] As shown in FIG. 4, an electrolytic cell (111) is composed of acation chamber (112) and an anion chamber (113), and a separationmembrane (114) dividing the cation chamber (112) and the anion chamber(113) is installed therebetween. In addition, inside the cation chamber(112) and the anion chamber (113), an anode plate (125) and a cathodeplate (126) are respectively installed.

[0055] In the cation chamber (112), brine is injected through a brineinjection tube (115), waste brine that remains after reaction andchlorine gas produced during electrolysis are stored in a cation chamberdischarge tank (117) after passing through a cation chamber dischargetube (116), chlorine gas is discharged again through a chlorine gasdischarge tube (118), and brine that remains after reaction andunreacted brine are discharged through a waste brine discharge tube(119).

[0056] In the anion chamber (113), pure water is injected through a purewater injection tube (120), and hydrogen gas and sodium hydroxideaqueous solution, reactants produced in the anion chamber (113), arestored in an anion chamber discharge tank (122) after passing through ananion chamber discharge tube (121). Hydrogen gas is discharged againthrough a hydrogen gas discharge tube (123), and a sodium hydroxideaqueous solution is discharged through a sodium hydroxide aqueoussolution discharge tube (124).

[0057] The method for electrolysis of the present invention ischaracterized by mixing an aqueous solution of a platinum compound withpure water and injecting the mixture in the anion chamber (113). Inorder to mix the aqueous solution of the platinum compound with purewater and inject it into the anion chamber (113), the aqueous solutionof the platinum compound is initially mixed with pure water and themixture is injected into the pure water injection tube (120), or aplatinum compound aqueous solution injection tube (127) connecting withthe pure water injection tube (120) is separately installed to injectthe aqueous solution of the platinum compound into the anion chamberthrough the platinum compound aqueous solution injection tube (127).

[0058] If the aqueous solution of the platinum compound is injectedthrough another injection tube of an electrolytic cell or through aplatinum compound aqueous solution injection tube connecting withanother injection tube, the objects of the present invention cannot besufficiently achieved. For example, if the platinum compound aqueoussolution injection tube is connected with the anion chamber dischargetube (121) and the aqueous solution of a platinum compound is injectedthrough it, most of the platinum in the platinum compound aqueoussolution is discharged to the anion chamber discharge tank (122) bydischarge pressure of the sodium hydroxide aqueous solution and hydrogengas discharged from the anion chamber, and thus the cathode plate (126)surface is not coated therewith.

[0059] However, the platinum compound aqueous solution is injected intothe anion chamber (113) through the pure water injection tube (120), theplatinum cation ingredient of the platinum compound aqueous solutionmoves to the cathode plate (126) by electrodeposition and is coated onthe cathode plate (126), and thus an electric resistance of the cathodeplate surface decreases to reduce power consumption for electrolysis.

[0060] The platinum compound is preferably selected from a groupconsisting of hexachloroplatinate (IV) (H₂PtCl₆. H₂O), potassiumtetrachloroplatinate (II) (K₂PtCl₄), diaminodinitroplatinum (II)(Pt(NH₃)₂(NO₂), hexaaminoplatinum (IV) chloride (Pt(NH₃)₆Cl₄),tetraamine platinum (II) chloride (Pt(NH₃)₄Cl₂), hydrogenhexahydroxoplatinate (IV) (H₂Pt(OH)₆), and sodium tetrachloroplatinate(II) (Na₂PtCl₄. 6H₂O). Hydrogen hexahydroxoplatinate (IV) (H₂Pt(OH)₆ ismost preferable because it is separated into platinum ions, hydrogenions, and hydroxide ions in an aqueous solution.

[0061]FIG. 2 shows a chemical equation involved in electrolysis of brineby injecting hydrogen hexahydroxoplatinate (IV) into an electrolyticcell. Brine is injected into a cation chamber, and pure water and aplatinum compound aqueous solution are injected into an anion chamber.

[0062] As shown in FIG. 2, Pt⁴⁺ platinum ions of the platinum compoundaqueous solution move to a cathode plate surface by electrodeposition.Platinum ions have superior electrical conductivity and corrosionresistance for strong alkali. In addition, a cathode plate plated withplatinum ions has comparatively low electric resistance compared to acathode plate plated with a material other than platinum ions or anunplated cathode plate, and it also has strong corrosion resistance fora strong alkali sodium hydroxide aqueous solution and thus can preventcorrosion of the cathode plate.

[0063] The contents of platinum compounds in the platinum compoundaqueous solution are preferably 0.1 to 10 wt %. If the contents are lessthan 0.1 wt %, an increase in electric resistance of a cathode platesurface cannot be prevented, and if the contents are more than 10 wt %,power consumption will not be simply proportional to the contents of theexpensive platinum compounds, thus making it uneconomical.

[0064] In addition, the amount of the platinum compound aqueoussolution. in the electrolyte composition for electrolysis of brine ofthe present invention comprising an aqueous solution of the platinumcompound is preferably 0.1 to 0.2 liter per 1 liter of pure waterinjected into an anion chamber. If the amount is less than 0.1 liter per1 liter of pure water, the amount of prepared sodium hydroxide will besmall, and if the amount is more than 0.2 liter, electrical resistanceof an electrode plate will not decrease in proportion to the amount ofexpensive platinum compounds, thus making it uneconomical.

[0065] The present invention also provides sodium hydroxide prepared bythe electrolysis method.

[0066] As shown in FIG. 4, if the platinum compound aqueous solution isinjected into the pure water injection tube to electrolyze brine, anaqueous solution of sodium hydroxide is produced in the anion chamber ofthe electrolytic cell. As a method for separating sodium hydroxide fromthe aqueous solution of sodium hydroxide, any method generally used inthe art can be employed.

[0067] The present invention also provides an apparatus for electrolysisof brine comprising a cation chamber and an anion chamber divided by aseparation membrane in an electrolytic cell; an anode plate and acathode plate respectively installed in the cation chamber and the anionchamber; a brine injection tube connected with the cation chamber; apure water injection tube connected with the anion chamber; and aplatinum compound aqueous solution injection tube connected with thepure water injection tube.

[0068] As explained, if brine is electrolyzed using the electrolytecomposition for electrolysis of brine comprising an aqueous solution ofa platinum compound and the method for electrolysis of brine of thepresent invention, electric resistance of an electrode plate can beminimized to reduce power consumption, and there is no need to interruptelectrolysis to separate an electrolytic cell in order to change anelectrode plate and thus the electrolysis process is efficient, the costrequired for maintenance and repair of an electrolytic cell can bereduced, and thus sodium hydroxide can be economically prepared. Inaddition, the method is environmentally acceptable because it does notinclude the heavy metal mercury, as does the mercury process.

[0069] The present invention will be explained in more detail withreference to the following Examples and Comparative Examples. However,these are to illustrate the present invention and the present inventionis not limited to them.

EXAMPLE 1

[0070] To 1 liter of pure water, 10 g of hexachloroplatinate (IV)(H₂PtCl₆. 6H₂O) were added to prepare an aqueous solution ofhexachloroplatinate (IV). The aqueous solution and pure water wererespectively injected into a platinum compound aqueous solutioninjection tube and a pure water injection tube in an electrolytic cell.Brine was injected into the electrolytic cell and an electrolytecomposition comprising the prepared platinum compound aqueous solutionwas injected into a cathode circulation tube for 3 minutes toelectrolyze brine to prepare a sodium hydroxide aqueous solution. Thetotal amount of injected pure water was 10 liters, and that of thehexachloroplatinate (IV) aqueous solution was 1 liter.

EXAMPLE 2

[0071] A sodium hydroxide aqueous solution was prepared by the samemethod as in Example 1, except that potassium tetrachloroplatinate (II)(K₂PtCl₄) was used as a platinum compound.

EXAMPLE 3

[0072] A sodium hydroxide aqueous solution was prepared by the samemethod as in Example 1, except that diaminodinitroplatinum (II)(Pt(NH₃)₂(NO)₂) was used as a platinum compound.

EXAMPLE 4

[0073] A sodium hydroxide aqueous solution was prepared by the samemethod as in Example 1, except that hexaaminoplatinum (IV) chloride(Pt(NH₃)₆Cl4) was used as a platinum compound.

EXAMPLE 5

[0074] A sodium hydroxide aqueous solution was prepared by the samemethod as in Example 1, except that tetraamine platinum (II) chloride(Pt(NH₃)₄Cl₂) was used as a platinum compound.

EXAMPLE 6

[0075] A sodium hydroxide aqueous solution was prepared by the samemethod as in Example 1, except that hydrogen hexahydroxoplatinate (IV)(H₂Pt(OH)₆) was used as a platinum compound.

EXAMPLE 7

[0076] A sodium hydroxide aqueous solution was prepared by the samemethod as in Example 1, except that sodium tetrachloroplatinate (II)(Na₂PtCl₄ 6H₂O) was used as a platinum compound.

COMPARATIVE EXAMPLE 1

[0077] A sodium hydroxide aqueous solution was prepared by the samemethod as in Example 1, except that 20 g of AuCl₃ were dissolved in 1liter of pure water instead of the platinum compound and the aqueoussolution thereof used, and the product AZEC MD66.69, manufactured byJapan Asahi Glass Co., Ltd was used as an electrolytic cell.

COMPARATIVE EXAMPLE 2

[0078] A sodium hydroxide aqueous solution was prepared by the samemethod as in Example 1, except that 20 g of RuCl₃ was dissolved in 1liter of pure water instead of the platinum compound, and the aqueoussolution thereof was used.

COMPARATIVE EXAMPLE 3

[0079] A sodium hydroxide aqueous solution was prepared by the samemethod as in Example 1, except that 20 g of IrCl₃ was dissolved in 1liter of pure water instead of the platinum compound, and the aqueoussolution thereof was used.

[0080] Comparison of Operating Voltage

[0081]FIG. 5 shows the operating voltages of the electrolytic cells ofExample 6 and Comparative Examples 1 to 3 with the lapse of operationtime. The initial operating voltages were all set to 6.65 V.

[0082] As shown in FIG. 5, when RuCl₃ and IrCl₃ aqueous solutions ofComparative Examples 2 and 3 were injected to electrolyze, the operatingvoltages of the electrolytic cells gradually increased with the lapse oftime. In addition, when adding the AuCl₃ aqueous solution of ComparativeExample 1 to electrolyze, the operating voltage increased more than inComparative Examples 2 and 3. It is considered that electric resistanceof the cathode plate increased due to Au, Ru, and Ir of the AuCl₃,RuCl₃, and IrCl₃ aqueous solutions injected into the anion chamber withthe lapse of the operation time.

[0083] However, when the platinum compound aqueous solution of Example 6was injected into an electrolytic cell to operate the electrolytic cell,the operating voltage decreased with the lapse of operation time.Particularly, after 15 minutes of operation, the operating voltagedecreased to 6.5 V, and then stabilized at 6.42 V. This is becauseplatinum cations of the hydrogen hexahydroxoplatinate (IV) (H₂Pt(OH)₆)aqueous solution were electrodeposited on a cathode plate surface byelectrodeposition to decrease electric resistance of the electrode platesurface.

[0084] As explained, if the platinum compound aqueous solution of thepresent invention is injected into a platinum compound aqueous solutioninjection tube connected with a pure water injection tube to electrolyzebrine, electric resistance of an electrode plate decreases and thusoperating voltage decreases, and therefore power consumption forelectrolysis can be reduced and sodium hydroxide can be economicallyprepared.

[0085] If brine is electrolyzed using the electrolyte composition forelectrolysis of brine comprising a platinum compound aqueous solutionand a method for electrolysis of brine using the same of the presentinvention, electric resistance of an electrode plate is minimized toreduce power consumption, there is no need to interrupt the electrolysisprocess to separate an electrolytic cell in order to replace anelectrode plate, and thus the electrolysis process is efficient and thecost required for maintenance and repair of an electrolytic cell can bereduced and sodium hydroxide can be economically prepared.

1. An electrolyte composition for electrolysis of brine comprising anaqueous solution of a platinum compound.
 2. The electrolyte compositionfor electrolysis of brine according to claim 1, wherein the platinumcompound is selected from a group consisting of hexachloroplatinate (IV)(H₂PtCl₆. 6H₂O), potassium tetrachloroplatinate (II) (K₂PtCl₄),diaminodinitroplatinum (II) (Pt(NH₃)₂(NO)₂), hexaaminoplatinum (IV)chloride (Pt(NH₃)₆Cl₄), tetraamine platinum (II) chloride (Pt(NH₃)₄Cl₂),hydrogen hexahydroxoplatinate (IV) (H₂Pt(OH)₆), and sodiumtetrachloroplatinate (II) (Na₂PtCl₄. 6H₂O).
 3. The electrolytecomposition for electrolysis of brine according to claim 1, wherein thecontents of the platinum compound in the aqueous solution of theplatinum compound are 0.1 to 10 wt %.
 4. The electrolyte composition forelectrolysis of brine according to claim 1, wherein the aqueous solutionof the platinum compound is used in the amount of 0.1 to 2 liters per 1liter of pure water.
 5. A method for electrolysis of brine, comprisinginjecting brine and pure water respectively to a cation chamber and ananion chamber divided by a separation membrane installed in anelectrolytic cell through a brine injection tube and a pure waterinjection tube, and applying a power source to an anode plate and acathode plate installed in the cation chamber and anion chamber toseparate produced chloride gas, hydrogen gas, and sodium hydroxideaqueous solution, characterized in that an aqueous solution of aplatinum compound is injected into the anion chamber through the purewater injection tube.
 6. The method for electrolysis of brine accordingto claim 5, wherein the aqueous solution of the platinum compound isinjected through a separate platinum compound aqueous solution injectiontube connected with the pure water injection tube.
 7. The method forelectrolysis of brine according to claim 5, wherein the platinumcompound is selected from a group consisting of hexachloroplatinate (IV)(H₂PtCl₆. 6H₂O), potassium tetrachloroplatinate (II) (K₂PtCl₄),diaminodinitroplatinum (II) (Pt(NH₃)₂(NO)₂), hexaaminoplatinum (IV)chloride (Pt(NH₃)₆Cl₄), tetraamine platinum (II) chloride (Pt(NH₃)₄Cl₂),hydrogen hexahydroxoplatinate (IV) (H₂Pt(OH)₆), and sodiumtetrachloroplatinate (II) (Na₂PtCl₄. 6H₂O).
 8. The method forelectrolysis of brine according to claim 5, wherein the contents of theplatinum compound in the aqueous solution of the platinum compound are0.1 to 10 wt %.
 9. The method for electrolysis of brine according toclaim 5, wherein the aqueous solution of the platinum compound is usedin an amount of 0.1 to 2 liters per 1 liter of pure water.
 10. Sodiumhydroxide prepared by the method of claim
 5. 11. An apparatus forelectrolysis of brine, comprising: a cation chamber and an anion chamberdivided by a separation membrane installed in an electrolytic cell; ananode plate and a cathode plate respectively equipped in the cationchamber and the anion chamber; a brine injection tube connected with thecation chamber; a pure water injection tube connected with the anionchamber; and a platinum compound aqueous solution injection tubeconnected with the pure water injection tube.
 12. Sodium hydroxideprepared by the method of claim
 6. 13. Sodium hydroxide prepared by themethod of claim
 7. 14. Sodium hydroxide prepared by the method of claim8.
 15. Sodium hydroxide prepared by the method of claim 9.